This invention related to improved backwashable filtering apparatus for machine tool lubricating coolants and the like, and more particularly to a novel filter element for use in such apparatus.
It has long been customary in connection with certain filtration systems, for example such as those employed for filtering machine tool lubricating coolants, to utilize a plurality of tubular filter elements for removing metal particles and the like from used fluid coolant before recirculating it back to the machine tools. During filtration the fluid is forced under pressure radially through the porous annular walls of the elements until the walls of the elements become unduly dirty or clogged. At that time the elements are momentarily disconnected from the system and are "backwashed" by pumping some of the previously filtered fluid in a reverse directon through the annular walls of the dirty elements, thus causing debris to be discharged from the element walls to a backwash outlet. Thereafter the cleaned elements are reinserted into the system line.
In one such prior apparatus (see for example U.S. Pat. No. 4,482,461), a plurality of tubular filter elements are mounted in a housing normally to be connected in the system line which contains the fluid under pressure that is to be filtered. The fluid is caused to pass into the bores of the elements, and then radially outwardly through the porous annular walls thereof to a common outlet. Whenever the pressure drop across the filter housing indicates that the elements are dirty, a tubular backwashing arm, which is mounted to rotate in one end of the housing, is rotatably indexed into communication with the adjacent ends of the tubular elements, one after the other, so that the elements are successively and momentarily subjected to a backwashing operation before being reinserted into the system line.
Known filtering apparatus of the type described has the disadvantage that it requires specially designed mechanisms for operating the indexible backwashing arm whenever a backwashing operation is necessary. Still another disadvantage of apparatus of this type is that only a portion of each tubular filter element is used at any instant, and each element tends to become plugged or clogged progressively, commencing from one end thereof and progressing toward its opposite end during a filtering interval--i.e., the interval of time during which a filter element is operatively connected in the system line. In other words, when a clear, tubular filter is first introduced into a system line, the radial flow to fluid from the inside to the outside of the filter is distributed over only a fraction of the total area of the filter element, normally adjacent the outlet end of the filter housing. As this area becomes plugged with dirt, the pressure gradient between the inside and the outside of the element seeks equilibrum by moving along the length of the tubular filter toward the opposite end thereof, thus causing the radial flow also to shift progressively toward the opposite end of the element until eventually the entire filter is dirty. At such time the pressure gradient suddently increases rapidly, thus indicating that a backwashing operation or the like is necessary in order to clean the element.
It is an object of this invention to provide for a filtration system of the type described, improved backwashable filtering apparatus which is substantially easier to manufacture and to operate than prior such apparatus.
More specifically, it is an object of this invention to utilize a special valving system for controlling the direction of flow of fluid through filter elements in backwashable apparatus of the type described, thus obviating the need for employing rotatably indexible backwashing arms of the type heretofore employed in such apparatus.
Still another object of this invention is to provide for use in backwashable filtering apparatus of the type described a novel filter element which is substantially more hydraulically efficient than prior such filter elements, and which is designed in such manner that the pressure gradient and flow of fluid during a filtering operation are distributed across the entire surface area of the element rather than across a portion only thereof.
Other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims, particularly when read in conjunction with the accompanying drawings.